Caso Clínico

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Ameloblastic fibroma versus hyperplastic follicular cyst
Fibroma ameloblástico versus quiste folicular hiperplásico

 

J. Azúa-Romeo¹, E. Saura Fillat², T. Usón Bouthelier², M. Tovar Lázaro³, J. Azúa Blanco⁴

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Resumen: El fibroma ameloblástico (FA) es un tumor odontogénico mixto, compuesto por tejido mesenquimal y epitelio odontogénico, representando el 2% de los tumores odontogénicos, mientras que el quiste dentígero o folicular (QF), el segundo quiste odontogénico en frecuencia, está compuesto exclusivamente por tejido conjuntivo laxo (mesénquima), si bien, el saco fibroso puede contener restos de epitelio odontogénico incluidos, dando lugar a una imagen histológica muy similar. La importancia de esta diferenciación radica en el tratamiento, que es ligeramente más agresivo en el FA y en el comportamiento biológico, ya que el FA puede derivar en un sarcoma ameloblástico, y el QF puede evolucionar hacia ameloblastoma y más raramente carcinoma mucoepidermoide. Palabras clave: Fibroma ameloblástico; Tumor odontogénico; Quiste folicular.

Abstract: Ameloblastic fibroma (AF) is a mixed odontogenic tumor composed of mesenchymal tissue and odontogenic epithelium, accounting for 2% of all odontogenic tumors, while dentigerous or follicular cyst (FQ), second odontogenic cyst in frequency, is formed exclusivelly by soft conective tissue (mesenchyme). Nevertheless, hiperplastic fibrous sac may contain rests of odontogenic epithelium, showing a similar histologic pattern. The importance of an adequate differentiation lies in the treatment, which is slightly aggresive for AF, and regarding the biological behaviour of both lesions, since AF might become in an ameloblastic sarcoma, while over an FQ could develope an ameloblastoma or even a mucoepidermoid carcinoma. Key words: Ameloblastic fibroma; Odontogenic tumor; Follicular cyst.

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1 Especialista en Anatomía Patológica. Profesor Asociado de Histología. Universidad de Zaragoza, España.
2 Médico Adjunto. Servicio de Cirugía Oral y Maxilofacial. Hospital Universitario Miguel Servet. Zaragoza, España.
3 Médico Adjunto. Servicio de Urgencias. Mutua de Accidentes de Zaragoza.
4 Especialista en Anatomía Patológica. Profesor Titular de Histología. Universidad de Zaragoza, España.

Correspondencia:
Dr. Javier Azúa-Romeo
Sº Anatomía Patológica (Banco de Tumores)
Hospital Universitario Miguel Servet
Pº Isabel la Católica 1 y 3
50009 Zaragoza, España.
Email: javierazua@hotmail.com

 

Introduction

We present the case of a 16 year old male who had an embedded wisdom tooth on the right side extracted. The subsequent histological study reported ameloblastic fibroma, benign mixed odontogenic tumor.

In this study we question the frequency of this entity (2% of odontogenic tumors) and give special attention to the differential diagnosis with the hyperplastic follicular cyst which shows similar histological characteristics.

This interest is based essentially on differering biological behavior and the therapeutic protocol that should be applied.

Clinical Case

A 16-year-old male patient, with no previous medical or odontological history of interest enquired about extracting an embedded wisdom tooth on the right side of the mandible for orthodontic reasons. The tooth had not shown any clinical inflammation. The orthopantomography (Fig. 1) showed a radiolucent image with radiopaque borders surrounding an unerupted molar. The lesion contained isolated pockets of calcified material. The overall image suggested the presence of an odontogenic cyst, and for this reason the macroscopic differential diagnosis included the dentigerous or follicular cyst (FC), calcifying odontogenic cyst, keratocyst and, as the least likely option, some type of odontoma.

The wisdom tooth was extracted, following an osteotomy, with local anesthetic. Exeresis of the pericoronal cystic-looking lesion was also carried out and it was sent for histopathologic study, as carrying out an intraoperative examination was not considered necessary. The tissue sample was routinely processed by means of staining with hematoxylin-eosin. The optical microscopical examination showed tissue with a myxoid appearance, together with clumps or threads of odontogenic epithelium. A study with more magnification showed loose connective tissue which revealed fusiform fibroblasts and macrophages, a well as cells typical of the tissue, and the previously reported islands of odontogenical epithelium, typically formed by two strands of epithelial cells with uniform morphology, with rounded or oval nuclei and limited eosinophile cytoplasm, with no evidence of malignancy or atypical transformation (Fig. 2). The post-surgical period was completely satisfactory, with no residual evidence of the lesion six months after the intervention.

Discussion

The first reference to ameloblastic fibroma was by Kruse in 1891.¹ Following this many cases and revisions have been published, and a frequency of between 1 and 3% of odontogenic tumors was established according to the series. Our experience discovered a much lower frequency which was not above 0.5% as, in the 500 patients studied from 1995, we have only come one case which is this one. The clinical characteristics of this tumor are very typical, significantly the average age is 12, with a superior age limit of 40. It appears with equal frequency in males and females, and it is most likely to found in the molar area of the mandible.²

These lesions are radiographically well defined, transparent, but with a halo which is more sclerotic and radiopaque. They can be unilocular or multilocular and they tend to be associated with the crown of the impacted tooth.³ If a more opaque area is observed within the lesion this guides the diagnosis towards ameloblastic fibro-odontoma, indicating the presence of a small odontoma, as the AF is completely lucent radiographically.¹

The definitive diagnosis is reached with a microscopical study, as loose connective tissue is found, of myxoid appearance, with fusiform cells (fibroblasts) and clumps or strands of odontogenic epithelial cells made up of cuboid cells, with rounded nuclei having no atypia, and a 2-3 cell thickness. In some cases the odontogenic epithelial cells continued their differentiation giving rise to the production of dentine and enamel, typical of fibro-odontoma, forming a pattern of compound or complex odontoma, which does not imply any difference in future treatment or biological behavior.

When the lesion has all the characteristics regarding age, localization and radiographic image, the initial diagnosis is quite simple. The problem arises when there is a failure in one of the characteristics.⁴ In this case our patient was within the age range and the localization was typical. However, the total absence of symptoms and the unspecific radiography did not guide us towards this type of tumor, but rather towards an odontogenic cyst. Therefore, the differential diagnosis should contain many entities, the most frequently included being ameloblastoma, odontogenic myxoma, dentigerous cyst, odontogenic keratocyst, central giant cell granuloma and histocytosis.

In this sense it would be easy to think that the final result lies in the hands of the pathologist who, with a minimum experience in oral pathology would be able to differentiate all the entities previously mentioned, in order to reach a definitive diagnosis of ameloblastic fibroma. We would like to stress the difficulty of histologic diagnosis and the need to give the pathologist all the relevant clinical data. Firstly, as we have already commented, there is the low incidence rate of AF, around 2% of odontogenic tumors, while on the other hand, the FC represents the second most frequent type of cyst in this localization. Therefore with this data it would be reasonable to first think of FC. The age of the patient is not of much help in this case, as both lesions are more frequent in the second decade of life, although the localization is very typical for AF, the radiography is also similar. In the case+ of FC lesions are more likely to be unilocular, radiotransparent and without peripheral sclerotic borders, including the impacted tooth.

The sample sent to the pathologist should be completely studied. One cannot «trust» an apparent benign appearance, and it is of great help including in the petition any impression as to the clinical diagnosis. In our case in particular, on carrying out the histological examination one of the fragments showed myxoid tissue with fibroblasts with no other accompanying cellularity. However, detailed analysis of tissue fragments revealed islands of epithelial tissue dispersed within the mesenchymal stroma, redirecting the diagnosis.

With etiopathogenic knowledge of these two entities it is easier to understand the biological behavior and evolution. The follicular cyst by definition consists exclusively of myxoid, loose connective tissue but the capsule which covers it presents typical odontogenic epithelium, which is stratified and squamous, and it includes some characteristic mucosecretory cells. In the development of the FC in which fluid is accumulated between the enamel and the dental crown, the odontogenic epithelium forms one of the walls of the cyst and, from this epithelium, remains can become detached and become trapped in the newly formed myxoid stroma.¹ It therefore consists of just one constituting tissue.

With AF, the major component is the primitive mesenchymal tissue, composed of clusters of connective tissue and similar-looking cells, with a capacity of converting themselves into any type of cellular line, and which, during the evolution of the tumor, will become odontogenic epithelial cells turning it into a benign mixed odontogenic tumor. For the correct diagnosis one of the key issues is the greater mesenchymal cellularity of the AF,^5-7 as well as the clusters of odontogenic epithelium distributed in a uniform manner through out the lesion, which is different to the follicular cyst in which these clusters are confined to the edge of the capsule.

We consider that many of the cases labeled as ameloblastic fibroma correspond in reality to hyperplastic FCs with epithelial inclusions.

With regard to AF treatment we accept that conservative treatment is the most suitable - removing the lesion and the impacted tooth should there be one, with curettage of the bone around the lesion. Bone curettage for FC appears not to be necessary. In the case we present curettage was avoided, as there was no previous indication to warrant this. In any event, once the anatomopathologic diagnosis was obtained, a second surgical procedure was not considered necessary. The patient is under periodic control and remains asymptomatic.

In both cases evolution and prognosis are favorable, although it is convenient to know that AF can turn into an ameloblastic sarcoma, and regarding FC malignancies in the form of ameloblasts have been described and, more rarely, mucoepidermoid carcinoma.⁵

In conclusion, all lesions of the oral cavity, including periodontal and salivary gland lesions, should be studied in detail, and one should not rely on their apparent benignity. Clinical, radiological and histological data should be integrated in order to adapt therapeutic and clinical protocol to the biological reality of the lesion.

References

 

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8. Azua-Romeo J, Uson T, Martinez-Tello A, Álvarez-Alegret R, Moral I. Epithelialmyoepithelial carcinoma arising from clear cell myoepithelioma of the parotid. Pathology 2002;34:475-7.         [ Links ]